1. Field of the Invention
This invention relates to an optical pick-up apparatus adapted to access different disks.
2. Description of the Related Art
An optical disc such as CD (Compact disc) and CD-R (CD-Recordable) is used to store audio, video and digital text information, as a recording medium. In recent years, optical discs have been developed to record larger amounts of information. To this end, there has become recently appeared a DVD (Digital Versatile Disc) capable of recording an amount of information relative to the CD and CD-R. A DVD is not only higher than the CD and CD-R in track density, but also shorter than those in a distance extending from the disc surface to the recording layer. The distance between the disc surface and the recording layer in a DVD is 0.6 mm while that in the CD and CD-R is 1.2 mm. Also, the recording layer of the DVD has characteristics different from that of the CD and CD-R. Due to such the structural differences with CD and CD-R, the DVD demands an optical pick-up apparatus different from the optical pick-up apparatus for the CD and CD-R. There are optical pick-up apparatuses for the DVD and for the CD and CD-R.
Optical pick-up apparatus are used to access the CD and CD-R as well as the DVD. Such a combined optical pick-up apparatus is shown in FIG. 1. The combined optical pick-up apparatus of FIG. 1 includes an objective lens 18 for allowing light beams B1 and B2 from a laser diode 12 and a hologram module 16 to be irradiated on the recording layer 10A or 10B of a disc 10, and a photo detector 14 for detecting light reflected by the information recording layer 10A or 10B of the disc 10. First information recording layer 10A represents the recording layer of a DVD, while second information recording layer 10B represents the recording layer of a CD or CD-R. The laser diode 12 generates a first light beam B1 having a wavelength of 650 nm adaptable to access the DVD. The photo detector 14 converts light reflected by the recording layer 10B of the DVD into an electrical signal. The hologram module 16 includes a laser diode (not shown) and a photo detector (not shown). The laser diode of hologram module 16 generates a second light beam B2 having a wavelength of 780 nm adaptable to access the CD and CD-R. The photo detector of the hologram module 16 detects the light reflected by the recording layer 10A of the CD or CD-R. A first beam splitter 20, a collimator 22 and a reflective mirror 24 are installed between the laser diode 12, the hologram module 16 and the objective lens 18. The first beam splitter 20 allows the first light beam B1 from the laser diode 12 and the second light beam B2 from the hologram module 16 to proceed in an identified path. To this end, the first beam splitter 20 not only reflects perpendicularly the first light beam B1 from the laser diode 12, but also passes the second light beam B2 from the hologram module 16. The collimator 22 forces the first and second light beams B1 and B2 each divergently transmitted from the first beam splitter 20 to proceed in parallel. The reflective mirror 24 reflects perpendicularly the first and second light beams B1 and B2 from the collimator 22 toward the objective lens 18. The objective lens 18 enables the first light beam B1 from the reflective mirror 24 to be irradiated on the first recording layer 10A of the disc 10 in the shape of a spot when the first light beam B1 is applied. Then, the DVD is normally accessed. If the second light beam B2 is input, the objective lens 18 irradiates the second light beam B2 from the reflective mirror 24 on the second recording layer 10B of the disc 10 such that the CD or CD-R is normally accessed. A second beam splitter 26 allows the light beam reflected by the disc 10 to be separately transmitted to the photo detector of the hologram module 16 and the photo detector 14, respectively. To this end, the second beam splitter 26 causes a part of the light beam from the collimator 22 to be passed toward the photo detector 14 and reflects perpendicularly the rest of the light beam from the collimator 22 toward the first beam splitter 20. The sense lens 28 converges the light beam to be proceeded from the second beam splitter 26 to the photo detector 14.
As described the above, the optical pick-up apparatus of FIG. 1 employs several optical elements for combining the optical systems for the CD/CD-R and DVD. In the optical pick-up apparatus, an aberration in the entire light path is great because the optical elements each generates an aberration. Also, the total aberration produced by the optical elements is greatest due to the combined manufacturing tolerance for each element. Consequently, the combined optical pick-up apparatus does not access accurately all the DVD, CD and CD-R.
Accordingly, it is an object of the present invention to provide an optical pick-up apparatus capable of accessing different discs with reduced aberration.
It is another object of the present invention to provide an optical pick-up apparatus capable of accessing different discs with a simplified configuration of elements.
In order to obtain the objects of the invention, according to one aspect of the present invention, an optical pick-up apparatus comprises: first light source for generating first light beam having first wavelength; second light source for generating second light beam having second wavelength; an objective lens for converging the first and second light beams on the recording layer of a recording medium in the shape of a spot; and a dichroic optical element for forcing the first and second light beams from the first and second light sources to proceed toward the objective lens along an identified path.
Further, according to other aspect of the present invention, an optical pick-up apparatus comprises: first light source for generating first light beam having first wavelength; second light source for generating second light beam having second wavelength; an objective lens for converging the first and second light beams on the recording layer of a recording medium in the shape of a spot; first and second photo detectors for detecting the first and second light beams reflected by the recording layer of the recording medium, respectively; and a dichroic optical element for forcing the first and second light beams from the first and second light sources to proceed toward the objective lens along an identified path and for distributing the light beam from the objective lens to the first and second photo detectors.